High density water-containing blasting materials containing ferrosilicon and ammonium nitrate



United States Patent HIGH DENSITY WATER-CONTAINING BLASTING MATERIALS CONTAINING FERROSILICON AND ANIMONIUM NITRATE Cliiford T. Butler, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Sept. 20, 1965, Ser. No. 488,774

11 Claims. (Cl. 14938) This application is a continuation-in-part of my copending application, Serial No. 395,316, filed September 9, 1964, which in turn is a continuation-in-part of application Serial No. 90,200, filed February 20, 1961, now abandoned.

This invention relates to high density water-containing inorganic oxidizer salt blasting compositions containing a smokeless powder as a sensitizer, and ferrosilicon in proportions for imparting high density to the composition. In another aspect this invention relates to watercompatible inorganic oxidizer salt explosive compositions capable of higher loading densities than heretofore.

Oxidizer salt type explosive compositions have had wide used in the art for some time. This type explosive, devoid of the liquid nitric ester and nitrocellulose components of conventional dynamites, is insensitive to detonation by a commercial blasting cap. Although ammonium nitrate is not necessarly employed as an oxidizer salt, it is often utilized in that capacity, alone or together with a supplemental oxidizer salt, such as sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate and the like. These type salts are highly water-soluble, and until recently, it has been the practice in the art to protect such oxidizer salt-containing compositions from direct contact with water and accompanying leaching action of the water. However, it has been found that these explosives can be detonated in the presence of water under certain conditions such as when employing a smokeless powder as a sensitizer therefor as disclosed and claimed in the copending application of Fred B. Clemens and Robert W. Lawrence, Serial No. 67,513, filed November 7, 1960, which in turn is a continuationin-part of US. application Serial No. 800,634, filed March 20, 1959, now abandoned.

Density of these water-compatible inorganic salt type explosives is, of course, of major importance in the use of these compositions in water-containing boreholes. Obviously, the higher the density, the greater is the ease in which the water-containing borehole is loaded. Density of the composition is also important from the standpoint of obtaining maximum loading density in the borehole, dry or water-containing, so as to thereby release a maximum of energy per unit length of the loaded portion of the hole.

Inorganic salt type explosive compositions of the above referred to copending applications are characterized by densities up to as high as about 1.7 grams per cc. However, unless special preparative precautions are taken and oxidizer salt and smokeless powder ingredients are selected from a narrow range of the highest particle densities, the density will more often be in the range of from about 1.2 to about 1.5 grams per cc.

3,235,424 Patented Feb. 15, 1966 This invention is concerned with inorganic oxidizer salt type blasting compositions characterized by densities as high as about 2 grams per cc. These compositions do not require special preparative procedures or limited selection of oxidizer salt and smokeless powder components in order to accomplish their high densities, and in view of their marked increase in densities, i.e., which are much higher than those of the said copending applications, they arecapable of loading densities higher than those heretofore possible for this type of explosive.

In accordance with the invention, high density watercompatible explosive compositions are provided which comprise, on a weight basis, from 25 to 75, generally, from 35 to 75, percent of an inorganic oxidizer salt, from 10 to 45, generally, from 10 to 35, percent of a-smokeless powder, from 2 to 16, generally, from 2 to 12, percent water, from 0.1 to 2.5 percent of a gel-forming agent for gelation of the water ingredient, and from about 12 to 30 percent of a ferrosilicon containing from 35 to percent silicon by weight.

By the term oxygen-supplying salt or oxidizer, as is well known in the explosives art, is meant one which, under the conditions of the detonation, liberates oxygen for the oxygen balance required. Ammonium nitrate is in some instances the only oxidizer salt component. However, other inorganic oxidizer salts can be used alone, in admixture with each other, or with ammonium nitrate as a supplementary oxidizer salt in any desired relative proportions. Of these supplementary salts, the alkali metal nitrates are now preferred. A now preferred oxidizer salt is a mixture of ammonium nitrate and sodium nitrate in a weight ratio of ammonium nitrate to sodium nitrate within the range of 0.521 to 2:1, particularly inasmuch as in these relative proportions, these mixtures lend themselves to generally preferred oxygen balance values.

Exemplary oxygen-supplying salts that can be used alone, or together with ammonium nitrate as supplemental oxidizer salt, are alkali metal and alkaline earth metal nitrates and perchlorates (including ammonium) as for example, sodium nitrate, magnesium nitrate, calcium nitrate, potassium nitrate, barium nitrate, sodium perchlorate, ammonium perchlorate, calcium perchlorate and magnesium perchlorate.

The gel-forming agent, i.e., one which forms a gel with the water components of the explosive composition, in order to prevent any settling of components and, in preferred practice, to impart a satisfactory degree of cohesiveness so that the composition retains its form as a unit mass in the presence of water for prolonged periods, is exemplified by sodium carboxymethylcellulose, mannogalactans, e.g., guar gum, methylcellulose, waterswellable starches and the like.

Natural guar gum and inhibited guar gum are now preferred gel-forming agents. By the term inhibited is meant that that particular guar gum contains an agent which prevents the guar gum from gelling immediately upon contact with the water, thus permitting the gum to disperse to a larger degree before gelation occurs, gelation of the natural gum being in many instances substantially instantaneous upon contact with the water. Exemplary inhibiting agents are hydrophobing materials particularly those capable of liberating borate ions, particularly sodium borate (borax).

By the term smokeless powder is meant the well known colloided nitrocellulose powders, the nitrocellulose in all events being characterized by a nitrogen content of at least about 11.3 weight percent, generally in the range of from about 12 to 13.5 percent, the powders being referred to in the art as single base, which is predominantly colloided nitrocellulose, double base, which is nitroglycerin-colloided nitrocellulose and triple base, which is nitroglycerin-colloided nitrocellulose-nitroguanidine.

Ferrosilicon, as is well known, is available in a wide range of iron to silicon ratios. However, in the accomplishment of the objectives of this invention, namely, the primary function of the ferrosilicon to impart high density together with improvement in explosive strength, the weight ratio of iron to silicon will generally be about 1:1 but can be varied over the range of values set forth hereinabove.

Particle size and type of the oxidizer salt ingredient is not generally critical. For example, ammonium nitrate can consist of prills such as used in fertilizer and which are substantially all on 20 mesh, or it can be granular and in that form, vary from coarse to fine. Other oxidizer salt components are generally of comparable granular particle size.

The particle size of the smokeless powder ingredient generally varies from about 20 mesh (100 percent through 20-mesh screen), through medium and coarse to perforated grains as large as, say about 0.5 inch long by 0.4 inch in diameter. Although a relatively fine particle size of smokeless powder component is often employed in the practice of the invention, the selection of particle size is, to a large extent, a matter of choice, depending upon the need at hand. Higher densities are obtained more readily with larger particle size smokeless powders and accordingly, the larger size is often preferred when applied to blasting in water-containing holes. In such event, more smokeless powder will be required for attaining a given sensitivity than if finer sized smokeless powder is utilized.

The now preferred compositions of the invention cornprise on a weight basis from 40 to 60 percent oxidizer salt, from about 0.2 to 1.5 percent guar gum as a gel-forming agent, from 15 to 30 percent of a smokeless powder, from 2 to 7 percent water and from 15 to 25 percent, often 15 to 20 percent, ferrosilicon containing silicon in the above described range of proportions often in about equal weights.

The compositions of the invention are insensitive to detonating action of a No. 8 commercial blasting cap, but are detonatable by conventional booster charges of PETN (pentaerythritol tetranitrate), RDX (cyclotrimethylenetrinitramine), Pentolite (PETNTNT, 50/50), tetryl, Composition B (RDXTNT, 60/40), gelatin dynamites and the like. One booster advantageously employed is a dispersion of a crystalline high explosive, e.g., PETN or RDX, in a plastic carrier such as described in the copending application of Alpheus M. Ball, Serial No. 538,788, filed October 5, 1955, and which is detonated by either a commerical blasting cap or a detonating fuse. It may also be advantageous to use Composition B, 60/40 RDX/TNT (cyclotal) or a cartridge of dynamite, preferably of a diameter approximating that of the borehole, as the booster.

Various sequences of steps for addition of the composition ingredients to the mixing chamber can be employed in the preparation of the explosive compositions of this invention. However, a preferred sequence involves adding the oxidizer salt, ferrosilicon and gel-forming agent ingredients to the mixing chamber followed by agitation for a short period, say 1-2 minutes; addition of the water at a temperature of about 140-160 F. followed by agitation for an additional short period, say 2-4 minutes;

and then addition of the smokeless powder with asubsequent agitation for about another 24 minutes.

The compositions of this invention are characterized by densities of from about 1.6 to 2.0 grams per cc., more generally above 1.7. Although without the use of ferrosilicon, density can be regulated in any given instance by selection of oxidizer salt and smokeless powder ingredients of the highest available densities together with a predetermined water content, selection of ingredients in this manner generally results in maximum densities not exceeding about 1.5 grams per cc. and in a few instances in values approaching 1.7. Further, such selection is often unduly limiting as to choice of the specific oxidizer salt and smokeless powder ingredients and is thereby limiting as to compositions that can be so prepared. By the presence of ferrosilicon in the compositions of the invention, densities up to about 2 grams per cc. are provided independently of the individual ingredient densities.

The presence of ferrosilicon in the minimum proportion provides for minimum densities of about 1.6, dependent upon the specific composition ingredients and proportions utilized and for inorganic oxidizer salt compositions of markedly higher densities than possible heretofore, and does so without any limitation as to choice of specific explosive ingredients and relative proportions thereof. The ferrosilicon ingredient also imparts thermal energy to the composition, thereby being advantageous over any inert high density ingredient that may be found to impart high density to the composition, i.e., without desensitization.

The high density explosives of the invention can be utilized in packaged form, i.e., as a cartridge or can be transferred into the hole as a unitary non-fluent plastic mass, and due to their high density, provide for loading densities higher than heretofore. This in turn reduces the number of boreholes needed in a given area for a given degree of breakage, or, if the same number of boreholes is utilized, they can be spaced over a larger area. In either event, the explosive force per unit loaded length of the borehole is markedly greater than has been possible for this type of explosive heretofore. The explosive compositions of the invention are highly resistant to freezing, i.e., down to temperatures in the order of 10 F. They can be stored over prolonged periods at 120140 F. without loss in sensitiveness and without exudation.

The explosives of the invention exhibit markedly high ability to maintain and propagate sensitiveness under high pressures and can be utilized under waterheads in the order of p.s.i. and higher.

The sensitivity of the explosive compositions is such that they can be advantageously used with delay firing under water without premature propagation from one charge to another. In underwater blasting of trenches, etc., it is frequently desirable to use delay or short period delay blasting in which successive charges are fired at intervals of 25-50 milliseconds, and it is important that the later charges be not set off prematurely by the shock from the charges which are fired first.

The following tabulation is illustrative of the explosive compositions of the invention (all shown on a weight percent basis), being particularly illustrative of the density properties and detonation characteristics. The detonation rate in each instance was determined by pouring the test charge into an iron pipe of diameter designated which is to give a degree of confinement comparable to that of drill holes used in commercial blasting. A booster charge was placed at one end of the pipe and initiated by a commercial blasting cap. Measurement of the detonation rate was made at a point beginning at least six charge diameters from the booster (to insure steady state conditions) and over an interval which insured that complete detonation of the column occurred. A standard counter chronograph system was used for measuring all detonation rates.

Sodium Nitrate 2 Calcium Nitrate 2 Ammonium Perchlorate 2 Smokeless Powder 3 Ferrosilicon 4 Guar Gum Density, grams per co Detonation (3 x 28" second (mps) Booster (gramsfi.

1 Substantially all through 40 mesh screen and substantially all on 100 mesh screen (mesh per inch).

2 GranularFine grade.

3 Examples 1-7, -20, 22-26, on weight percent basisNitrocellulose (13.15% N), 97.7; diphenylamine, 0.80; potassium sulfate, 0.75; and tin, 0.75. Grains 0.04" diameter x 0.10 long. One perforation, 0.008 diameter. Example 21, on weight percent basis-nitroceullulose (13.15% N), 90; diphenylamine, 1.0; dibutylphthalate, 2.0; DNT, 1.0. Grains, 0.08 diameter x 0.3 long. One perforation.

Examples 8-9 on weight percent basis-Nitrocellulose (13.15% N), 58.75; nitroglycerin, 40.0; and ethyl Centralite, 1.25. Non-perforated grain, .038" diameter x 0.0026 long.

The blasting compositions of this invention are further characterized by their high sensitivity when under high pressure even after prolonged standing under such conditions as demonstrated with reference to Example No. which shows detonation of the described composition at 5240 m/sec. after standing at 300 p.s.i.a. for 24 hours. This is in contrast with conventional gelatin dynamites, which rapidly lose sensitivity when retained under such pressure, as described in U.S. 2,365,170, issued to Bitting et al.

As briefly discussed hereinabove, smokeless powder herein refers to colloided nitrocellulose powders. As is well known, the single base powder contains colloided nitrocellulose as the chief component, say in the order of from about 85 to 99 weight percent and the double base powder contains the same colloided nitrocellulose component but together with nitroglycerin or an equivalent liquid explosive nitric ester. Double base powders contain generally at least one-third colloided nitrocellulose and substantially the remainder nitroglycerin, with, of course, the usual supplemental ingredients. Triple base powders contain nitroguanidine in addition to the colloided nitrocellulose, and nitroglycerin, in proportions generally at least about to percent nitroguanidine and substantially as the remainder colloided nitrocellulose and nitroglycerin, the latter two being in any suitable relative proportions, for example, 1:1 to 4:1 of nitrocellulose to nitroglycerin.

Minor amounts of supplemental ingredients are utilized in these powders, particularly stabilizing agents, gelation agents, oxidizer salts, in some instances DNT oil and the like, all as Well known in the art. Smokeless powder is manufactured in the form of small flakes, strips, pellets, granules and cylindrical grains, the latter being generally perforated.

Various procedures have been utilized in the manufacture of this type of smokeless powder. Thus, in the usual solvent process, which generally utilizes a water-wet nitrocellulose as raw material, the water in the nitrocellulose is first replaced, for example, by treatment with ethyl 17 ge lssi-Examples 1-15, 18, 19-26, 1:1; Example 16, 65:35; and Example 5 Examples 1-9, 11, 12, 16, 17PETN (pentaerythritol tetranitratc). Examples 10, 13-15, 18 and 19-Compositi0n B (RDX/TNI, 60/40). Examples 2026-Pentolite (TNT/PETN, 50/50).

6 Estimated.

1 Estimatedno shot made.

Also contained 0.1 weight percent pine oil as a surfactant.

9 Barium Nitrate in lieu of Calcium Nitrate.

Sodium Perchlorate in lieu of Ammonium Perchlorate.

11 Except Example 20 wherein shot was made in a 2 x 28 pipe, after standing 24 hours under 300 p.s.i.g.

alcohol. A colloiding solvent such as ether or acetone is then added to the dehydrated alcohol-wet nitrocellulose along with the additional ingredients and a doughy mass is formed in a suitable mixer such as a Sigma blade mixer. This dough is then formed into green grains, usually by extrusion into cords followed by cutting the cords to the desired length. The green grains are then subjected to solvent removal steps, including vaporization, water leaching and drying.

Exemplary of the smokeless powder formulations contemplated in the practice of the invention are:

Weight Per Cent Single Base Double Base Triple Base Nitrocellulose 99. 0 83.0 90.0 93. 8 59 0 78. 3 20. 0 Nitroguanidine 54. 7 N itroglycerin 5. 0 40. 0 20. 0 19. 0 Diphenylamine 1. 0 1. 0 1. 0 0. 7 0. Dinitrotoluene 10.0 8.0 Dibutyl phthalate 5.0 Potassium Sullate 1. O 1. 0 1. 0 1. 0 Ethyl Centralite... 1.0 6.0 Cryolite* 0. 3

*BNaF-AlFg.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What I claim and desire to protect by Letters Patent is:

1. As a water-compatible blasting composition, on a weight basis, from 35 to percent of an inorganic oxidizer salt, from 10 to 35 percent of a smokeless powder, from 2 to 12 percent water, from about 0.1 to about 2.5 percent of a gel-forming agent for gelation of the above said water ingredient, and from about 12 to 30 percent of a ferrosilicon containing from 35 to 75 weight percent silicon.

2. A composition of claim 1 containing from 2 to 7 percent water, from 40 to 60 percent of said oxidizer salt, and from to 30 percent of said smokeless powder, from 0.2 to 1.5 percent of guar gum as said gel-forming agent, and from 15 to percent of said ferrosilicon.

3. A composition of claim 2 wherein said ferrosilicon contains iron and silicon in substantially equal weight proportions.

4. A composition of claim 2 wherein said oxidizer salt is a mixture of ammonium nitrate and sodium nitrate and contains ammonium nitrate in a weight ratio to said sodium nitrate within a range of from 0.5:1 to 2: 1.

5. A composition of claim 1 wherein the said oxidizer salt consists of ammonium nitrate.

6. A composition of claim 1 wherein the said oxidizer salt consists of sodium nitrate.

7. A composition of claim 1 wherein the said oxidizer salt consists of calcium nitrate.

8. A composition of claim 1 wherein the said oxidizer salt consists of ammonium perchlorate.

9. A composition of claim 1 Containing up to percent of said ferrosilicon.

10. A composition of claim 2 characterized by a bulk density of from 1.7 to 2.0 grams per cc.

11. As a water-compatible blasting composition, on a weight basis, from 25 to 75 percent of an inorganic oxidizer salt, from 10 to 45 percent of a smokeless powder, from 2 to 16 percent water, from about 0.1 to about 2.5 percent of a gel-forming agent for gelation of the above said water ingredient, and from about 12 to percent of a ferrosilicon containing from to weight percent silicon.

No references cited.

LEON D. ROSDOL, Primary Exmnincr.

BENJAMIN R. PADGETT, Assistant Examiner. 

1. AS A WATER-COMPATIBLE BLASTING COMPOSITION, ON A WEIGHT BASIS, FROM 35 TO 75 PERCENT OF AN INORGANIC OXIDIZER SALT, FROM 10 TO 35 PERCENT OF A SMOKELESS POWDER, FROM 2 TO 12 PERCENT WATER, FROM ABOUT 0.1 TO ABOUT 2.5 PERCNET OF A GEL-FORMING AGENT FOR GELATIN OF THE ABOVE SAID WATER INGREDIENT, AND FROMABOUT 12 TO 30 PERCENT OF A FERROSILICON CONTAINING FROM 35 TO 75 WEIGHT PERCENT SILICON. 